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OCR Chemistry A Exam Thread (Breadth - May 27 2016 and Depth - June 10 2016) Watch

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    (Original post by Mariamjaan)
    Attachment 541077

    Hey,,, can anyone help me with empirical formula, I did it but it is wrong.

    Thanks
    C:
    88.89/12=7.4075
    H:
    11.1/1=11.1
    Therefore ratio =1:1.5 =2:3 so empirical is C2H3

    Then you need to look at the molecular ion peak which is 54 however C2H3 is only 27 so that means the molecular formular is C4H6

    Then look at the reaction:
    Compund x reacts with H2 in the ratio 1:2
    So C4H6+2H2
    This means that there are 2 double bonds being broken and hence you have the structure
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    Does anyone have those exam-style questions worksheets? They're in kerboodle somewhere I think but I'm guessing they're only accessible by teachers? Heaven knows why, they seem like such good resources for the depth paper.
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    Does anyone know if there is a possibility of being questions with more than 6 marks on the breadth paper? The specimen only has 6 mark questions, but one of the old papers had a 12 mark question (jan 2013, f322).
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    (Original post by Internets)
    Does anyone know if there is a possibility of being questions with more than 6 marks on the breadth paper? The specimen only has 6 mark questions, but one of the old papers had a 12 mark question (jan 2013, f322).
    I'd say it's possible. On OCR these usually aren't an issue - you can think of them as being like 12 1-mark questions, rather than an AQA-style essay.
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    Just a little resource I created. I checked through the specification and tried to find small/subtle facts and requirements that many people might skip over and miss. I can't promise I got them all but I got most but I would recommend that you all go and check the specification. I didn't exactly explain all the points here as it was more a way to identify of you don't know the facts so you can go revise them but feel free to ask if you need help. Name:  1464796244326.jpg
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    (Original post by alfmeister)
    Just a little resource I created. I checked through the specification and tried to find small/subtle facts and requirements that many people might skip over and miss. I can't promise I got them all but I got most but I would recommend that you all go and check the specification. I didn't exactly explain all the points here as it was more a way to identify of you don't know the facts so you can go revise them but feel free to ask if you need help. Name:  1464796244326.jpg
Views: 568
Size:  64.6 KBName:  1464796277496.jpg
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    This was very useful. Thank you
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    (Original post by Floodeagle)
    This was very useful. Thank you
    Glad I could help!
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    (Original post by Floodeagle)
    This was very useful. Thank you
    Hi few questions, why does the actual bond enthalpy differ from the one stated ?
    How do you explain the small differences in first ionisation energies in an exam style ?
    How do you rearrange Kc and PV=nRT ?

    Also a good anagram for remembering the tests is CASH carbonate, ammonia, sulfate and halide correct me if I'm wrong. Thanks for this post!
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    (Original post by ChiefNik)
    Hi few questions, why does the actual bond enthalpy differ from the one stated ?
    How do you explain the small differences in first ionisation energies in an exam style ?
    How do you rearrange Kc and PV=nRT ?

    Also a good anagram for remembering the tests is CASH carbonate, ammonia, sulfate and halide correct me if I'm wrong. Thanks for this post!
    1)The average bond enthalpy is different from the actual bond enthalpy because the average bond enthalpy is the energy required to to break one mole of a specified type of bond in a gaseous molecule.Therefore, the bonds broken are not always from the same molecule. For example, in OH bonds it's enthalpy is different in a molecule of water in comparison to in ethanol.

    2) There is a slight decrease in ionisation energy from nitrogen to oxygen as the the extra electron in oxygen pairs up with the first electron forming a pair of electrons and completing a 2p orbital. Removing one electron from a pair requires slightly lower energy than removing a lone electron because the paired electron repel one another making it easier to remove one.

    (sorry for the difference in image size)

    3) When using the ideal gas equation you are trying to isolate the variable which is unknown. Therefore if you are trying to find the number of moles (n) then you would divide by R and T leaving:

    n = PV / RT
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    I think i got 58-62 would 58 be an A?
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    Does anybody have the mark schemes to the 2015 past papers for ocr??
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    (Original post by alfmeister)
    1)The average bond enthalpy is different from the actual bond enthalpy because the average bond enthalpy is the energy required to to break one mole of a specified type of bond in a gaseous molecule.Therefore, the bonds broken are not always from the same molecule. For example, in OH bonds it's enthalpy is different in a molecule of water in comparison to in ethanol.

    2) There is a slight decrease in ionisation energy from nitrogen to oxygen as the the extra electron in oxygen pairs up with the first electron forming a pair of electrons and completing a 2p orbital. Removing one electron from a pair requires slightly lower energy than removing a lone electron because the paired electron repel one another making it easier to remove one.

    (sorry for the difference in image size)

    3) When using the ideal gas equation you are trying to isolate the variable which is unknown. Therefore if you are trying to find the number of moles (n) then you would divide by R and T leaving:

    n = PV / RT
    Thanks for this!
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    (Original post by Lauryn_C)
    Does anybody have the mark schemes to the 2015 past papers for ocr??
    F321: Paper | Mark Scheme
    F322: Paper | Mark Scheme
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    Does anybody have a list of the practicals we need to know how to do from the OCR booklet ?
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    (Original post by ChiefNik)
    Does anybody have a list of the practicals we need to know how to do from the OCR booklet ?
    I have a list of all the practicals and answers to the questions. I can email them to you. PM me
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    (Original post by marioman)
    I think I've said this three times now: they are introducing new Admissions Assessments which will replace the role of UMS.
    I emailed ocr and they said that you wont get ums just a grade with no raw marks but your school could give you a breakdown of marks if you want.
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    (Original post by ineedA)
    I think i got 58-62 would 58 be an A?
    Definitely. Unless the grade boundaries are stupidly high this year, which i doubt they will be
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    (Original post by 4nonymous)
    C:
    88.89/12=7.4075
    H:
    11.1/1=11.1
    Therefore ratio =1:1.5 =2:3 so empirical is C2H3

    Then you need to look at the molecular ion peak which is 54 however C2H3 is only 27 so that means the molecular formular is C4H6

    Then look at the reaction:
    Compund x reacts with H2 in the ratio 1:2
    So C4H6+2H2
    This means that there are 2 double bonds being broken and hence you have the structure


    Thank you😊
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    What does the specification mean by this:

    The benefits for sustainability of processing waste polymers by: (i) combustion for energy production (ii) use as an organic feedstock for the production of plastics and other organic chemicals (iii) removal of toxic waste products, e.g. removal of HCl formed during disposal by combustion of halogenated plastics (e.g. PVC). HSW9,10 Benefits of cheap oil-derived plastics counteracted by problems for environment of landfill; the move to re-using waste, improving use of resources.
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    Anyone's got any tips for time management for the depth paper?
 
 
 
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